Sheet transport device

ABSTRACT

The invention relates to a sheet transport device, preferably for arrangement on the sheet-delivery side of a printing machine, including at least two rollers that are axis-parallel with respect to each other and form between them a transport gap for the sheets for a reversible deformation and stiffening of the sheets respectively transported between them. The rollers are such that a sheet which exceeds a specific intrinsic stiffness is able to move the rollers apart against the applied force in order to avoid said sheet&#39;s deformation and/or in order to enlarge the diameter of the second roller, viewed in side elevation of the second roller, a rounded transition has been implemented in at least one section.

CROSS REFERENCE TO RELATED APPLICATIONS

Reference is made to and dual priority claimed from:

German Application No. 10 2005 013 756.3, filed on Mar. 22, 2005,entitled: PAPER TRANSPORT ROLLER; and

German Application No. 10 2005 013 757.1, filed on Mar. 22, 2005,entitled: PAPER TRANSPORT ROLLER.

FIELD OF THE INVENTION

The invention relates to a sheet transport device, preferably forarrangement on the sheet-delivery side of a printing machine,specifically an electrophotographically operating printing machine,comprising at least two rollers that are axis-parallel with respect toeach other and form between them a transport gap for the sheets. Therelative distance between said rollers being variable in that therollers and/or zones of the rollers can be crossed or staggered relativeto each other for a reversible deformation and stiffening of sheetsrespectively transported between them, and a force being applied towarda magnification or increase of said crossing of the rollers and/or theroller zones, and the deformation of the sheet being pre-specified.

BACKGROUND OF THE INVENTION

A device of the aforementioned type has been disclosed by U.S. Pat. No.5,653,439. This patent discloses axis-parallel stiffening rollers,whereby their distances can be varied relative to each other, in whichcase the rollers of one of the axles are spring-biased in the directiontoward the rollers of the other axle. This spring bias is intended toensure that the slippage of the rollers adapts automatically to printingmaterials having different thicknesses or different weights per unitarea. In so doing, all printing materials are deformed, transported, anddeposited at approximately the same speed or deceleration.

When using this device, however, undesirable effects may occur. Forexample, in particular, a thinner sheet of printing material couldpotentially not be sufficiently (stiffly) transported out of theinventive device, for example, before its leading edge arrives on astack of sheets deposited on the delivery side of a printing machine,thus shifting sheets that have already been deposited on the stack, orsaid sheet could fold over too soon and thus cause a printing materialjam; also, a thicker sheet could be irreversibly deformed and its shapeor printed image could be damaged.

Therefore, the object of the invention is to provide a device of theaforementioned type, which ensures sufficient stiffening of therespective sheet, on the one hand; and treats, in particular, thickersheets in a sufficiently gentle manner, on the other hand.

SUMMARY OF THE INVENTION

In accordance with the invention, this object has been achieved in thatthe rollers are arranged and configured and the application of force isset or selected in such a manner that a sheet which exceeds a specificintrinsic stiffness is able to move the rollers apart against theapplied force in order to avoid said sheet's deformation.

Therefore, considering the inventive stiffening device, a sheet isadvantageously deformed only then, and only to an extent as is requiredor desirable for complementing its intrinsic stiffness, while sheetsexhibiting sufficient intrinsic stiffness may remain completelyundeformed and are transported flat through the device in order toavoid, in particular, damage due to an irreversible deformation of suchsheets, this risk being particularly great regarding such sheets. Inaccordance with the invention this is achieved in that the applicationof force is adapted thereto in a pre-specified manner to allow therollers to spread apart far enough in order to eliminate crossingbetween them altogether, if necessary.

In so doing, the application of force is adjusted or selected withrespect to the weight of the paper per unit area, in particular, when asheet of paper is concerned. In particular, as regards other materials,another parameter that influences the intrinsic stiffness can be used ascriterion, for example, the thickness. In so doing, the type ofarrangement of the rollers and/or the application of force can beadapted to the parameter in a non-linear manner, for example, by guidingcams or power-pack staggering.

In as much as a sheet must not be deformed beginning with a specificweight per unit area, because in the case of such a sheet the risk ofirreversible deformation is too great, a guide value for such a sheetmay be specifically determined in that the application of force is setor selected relative to the force applied to a sheet having a weight perunit area which is greater than or equal to approximately 220 grams persquare meter.

Likewise, a second, lower guide value can be determined for a sheetwhich is to be deformed to its maximum in each instance, because saidsheet, in addition, must be stiffened by a deformation because itsintrinsic stiffness is not sufficient, in that the application of forceis set or selected in such a manner that a sheet having a weight perunit area of greater than or approximately equal to 100 grams per squaremeter is deformed to its maximum.

A modification of the invention provides that one of the rollers isdriven by a shaft, while the other roller follows on its axle, in whichcase the follow-roller preferably is subject to the application ofpressure in the direction toward the driven roller.

Preferably, force is applied to the roller in the higher location, saidroller's inherent weight contributing to the applied force. The appliedforce can be set in such a manner that, taking into consideration theinherent weight of the roller to which the force is applied, saidapplied force corresponds to a weight of approximately 400 grams. Then,in particular, this force is great enough in order to sufficientlystiffen relatively thin sheets and small enough to yield appropriatelyto the intrinsic stiffness of relatively thick sheets, thus avoidingirreversible buckling of the sheets. If force is applied to the upperroller, its inherent weight must be considered as an increase of force;and if force is applied to the lower roller, its inherent weight must beconsidered as a decrease of force.

A further modification of the invention provides that a plurality ofrollers is arranged on each of the axles, said rollers being capable ofmeshing, in which case, specifically a zipper-like meshing of teeth ofthe rollers is conceivable, whereby respectively one roller of one axiscomes into engagement with a gap between two rollers of the other axis.Of course, this meshing may also take place by following anotherpattern.

One further modification which claims independent protection andindependently achieves the object of the invention is characterized inthat two rollers have profiles that are in engagement with each other inthe transport gap, whereby the profile of a first roller has a reduceddiameter in a central region, while the profile of a second roller hasan enlarged diameter in an approximately corresponding region such thatthe profile engagement can serve for stiffening a respective sheettransported through the transport gap. As a result of this inventivedevelopment, it is not necessary to cross or stagger all the rollersrelative to each other, but such crossing and staggering may relate tosections of the profiles of individual rollers and thus result insufficient stiffening of the sheets. In so doing, it is also possible toimprove stiffening by a pre-specified optimized roller contour and thusensure a gentle treatment of the sheets, in particular thicker sheets.

In accordance with the invention, this object has been achieved in that,in order to enlarge the diameter of the second roller, viewed in sideelevation of the second roller, a rounded transition is implemented inat least one section.

As a result of this, an individual sheet is transported in a gentlermanner, but still preferably also better stiffened, in order to push itas far as possible out of the device, so that preferably approximatelyslightly more than two-thirds of its transported length project freely.

Considering this inventive roller contour, the respective sheet istransported in a surprisingly simple yet effective manner, not only in amore gentle, but also in a better stiffened manner, this applying, inparticular, to sheets having very different formats and/or weights perunit area.

Preferably, in accordance with the invention, the second roller has adiameter maximum and is provided on both sides of said diameter maximumin at least one section with a rounded transition in order to enlargethe diameter of the second roller, viewed in side elevation of thesecond roller, in which case, preferably, also the first roller has adiameter maximum, and the rollers are configured symmetrically withrespect to a respective diameter extreme.

It has been found that different possibilities exist for providing aninventive, rounded contour of the second roller. To achieve this, afirst advantageous embodiment provides that, in the case of the secondroller, the rounded transition bulges toward the outside of the roller.Thus, the contour extends in an essentially convex manner toward theoutside. In so doing, the second roller may overall have essentiallyapproximately the shape of a barrel or be essentially spherical. Inaddition, however, in order to provide a more distinct diameter maximum,a central region may protrude outward approximately in the shape of atire. Considering each of these described embodiments, tests have shownthat such a tire should not be too narrow, in order to avoid creasing ofthe respective sheet. The width of such a tire, for example, could bewithin the size range of approximately 7 millimeters. Consideringcreasing of a sheet, under certain circumstances, the coefficient offriction with respect to the sheet material is also a noteworthyparameter. In conjunction with this it has been found that it is betterif the coefficient of friction of the rollers, specifically the secondroller, is somewhat lower. Then, creasing of the sheet is insignificantand, as a result of the deformation of the sheet, there is no excessiveslippage during sheet transport. In addition, the rollers may havedifferent coefficients of friction or have regions exhibiting relativelydifferent coefficients of friction.

A second advantageous embodiment of the inventive second roller providesthat, in the case of the second roller, the rounded transition isconfigured in a cheek-like manner or is concavely bulging inward, inwhich case, preferably inward-bulging and outward-bulging roundedtransitions may be provided so that successive transitions following thecontour of the second roller preferably have, or result in, the shape ofa bell.

A third advantageous embodiment of the inventive second roller providesthat the second roller has at least one bead-like thicker region. As aresult of this, the second roller could also be largely cylindrical.Likewise, the second and third embodiments may provide that, in order tocreate a more distinct diameter maximum, a central region protrudesoutward approximately like a tire. For example, the type of contour tobe selected could be a function of the material used for the printingmaterial, in which case, specifically in electrophotographic printing, alarge spectrum of printing materials may potentially be used, e.g., notonly paper but also film materials, for example. The inventive rollerscan also be designed for easy exchange and arrangement.

In order to allow the first and second rollers to be in a certainengagement with each other, the first roller must display a reduction indiameter approximately in the region where the first roller displays anenlargement in diameter, even though it is by no means necessary toachieve gapless meshing. On the contrary, it has even been found that,in particular in the central region, a larger gap between the rollersand thus a larger free space for deforming the sheet can beadvantageous.

In as much as, preferably in the central region, the second rollershould have an enlarged diameter and, correspondingly, the first rollershould have a reduced diameter, a preferred embodiment of the firstroller provides, in accordance with the invention, that the first rollerhas approximately the shape of a dumbbell. Considering this type ofshape, it is particularly easily possible to allow an appropriate gap tobe left open in the central region between the rollers.

The first roller, the second roller, or both rollers, may be assembledof several parts. For example, at least one of the rollers may comprisedisks or disk segments, e.g., even having different coefficients offriction and consisting of different materials. Even tires, rings,linings or the like would be conceivable. In this context, it should besaid, that the rollers need not necessarily be absolutely rotationallysymmetrical.

In particular, the dumbbell shape of the first roller, could beimplemented by two spaced apart rollers, in such a manner, that thecentral region would be the axle or shaft itself. Even segments of thesecond roller could optionally spaced apart from each other. In suchinstances, it is of course possible to speak of several rollers, which,by interacting, form a roll profile of one metal roll, as it were.

A subsequent development of the invention provides that the first rollerhas at least one region, which is substantially rounded in a mannerapproximately complementary to at least one rounded transition of thesecond roller. Advantageously, this results, at least in the roundedregion(s), in gaps for the respective sheets, said gaps havingboundaries extending in the same manner and exhibiting consistent width,in order to guide and shape the sheet in an optimal manner specificallyin these regions. Considering the second roller, the affected regionsmay be specifically side regions, which are associated withcorrespondingly formed running or run-off paths. As provided by adevelopment of the invention, these paths may be located in the regionsof the dumbbell heads of the dumbbell shape of the first roller.

In a preferred embodiment of the inventive device the second roller isthe follow-roller.

Another preferred embodiment of the inventive device provides that thedevice is configured for inclined upward-oriented transport or such anejection or delivery of the respective sheet, e.g., at an angle ofapproximately 22 degrees.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments that could result in additional inventive features, which,however, do not restrict the scope of the invention, are shown by theschematic drawings. They show in:

FIG. 1 a first embodiment of rollers out of engagement with each other,in side elevation;

FIG. 2 said first embodiment in engagement with each other, in sideelevation;

FIG. 3 a second embodiment of rollers in engagement with each other, inside elevation;

FIG. 4 said second embodiment during transport of a thicker sheet, outof engagement; and

FIG. 5 a third embodiment of an inventive roller as the contour showingan example of dimensions.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a first embodiment of a region of an inventive device withrollers 1, 2 out of engagement with each other, in side elevation.Rollers 1, 2 are arranged opposite each other on axles 3, 4 that areparallel to each other and staggered with respect with each other. In sodoing, axle 3 can be configured as the driven shaft, which supports thefirst rollers 1 in a drivable manner, whereas the second rollers 2 maybe arranged so as to follow and be freely rotatable on axle 4. Indicatedbetween rollers 1, 2 is a thick sheet 13, which is driven andtransported by the first rollers 1, whereas the second roller 2 in thiscase only rolls off the sheet and, in this manner, follow the firstrollers 1 and, in so doing, act only as a type of transport boundary forforming a transport gap between the rollers 1 and 2. In particular thisthick sheet 13 is not deformed because such a deformation of a thicksheet 13 could be irreversible.

In so doing, rollers 1, 2, considering their (in this case,substantially oval) profile, are suitable to wave or deform sheetsduring transport such that said sheets are stiffened. This is clearlyshown by FIG. 2, which, in comparison with FIG. 1, is meant to show athin sheet 18 between rollers 1, 2.

FIG. 2 indicates that the second rollers 2 can be movably supported inaxial direction in their respective hubs as indicated by double arrows17, or axle 4 itself could be arranged movably in the direction of adouble arrow 16. In addition, a force is applied to the second rollers 2or to axle 4 in the direction of axle 3.

The thin sheet 18 in FIG. 2 possesses only a relatively low intrinsicstiffness (different from thick sheet 13 in FIG. 1), so that axle 4 mayyield to the force exerted by said intrinsic stiffness and the thinsheet 18 is not capable of pushing back the second rollers against thisforce. Consequently, a wave-shaped maximum deformation of thin sheet 18occurs during said sheet's transport between rollers 1, 2. In so doing,rollers 1, 2 are meshing in a zipper-like manner with each other, orthey are crossed or staggered relative to the respectively adjacentroller on the other axle. In order to avoid such waving in the case of athick sheet 13, it is specifically not only necessary to tune theapplication of force, but it must also be possible to push back thesecond rollers 2 until they are disengaged, without preventing this byan abutment stop, for example. Therefore, potentially an adjustableguide and/or abutment guide for the second roller 2 and/or its axle 4 isadvantageous.

FIG. 3 shows a schematic view of a second embodiment of inventiverollers in engagement with each other, in side elevation.

The section of an inventive device shown in FIG. 3 comprises a firstroller and a second roller 2, which are provided for a sheet transportand are in a certain engagement with each other by means of theirprofiles in order to (reversibly) deform and thus stiffen sheetstransported by said rollers 1, 2. The first roller 1 is rotatablysupported by a axle 3, whereas, the second roller 2 is arranged in afreely rotatable manner on an axle 4 and follows or rotates along withthe first roller 1 during the transport of a respective sheet betweenrollers 1, 2. In so doing, the second roller 2, or its axle 4, isarranged again so as to move in the direction of double arrows 16, 17and a force is applied on said roller 2, or said axle 4, in thedirection toward axle 3.

In FIG. 3, the second roller 2 has a continuously rounded contour, whichleads to a maximally enlarged diameter of the second roller 2 in itscentral region. In said central region, the second roller 2 has anoutward-bulging convex rounded section 5. On both sides, andsymmetrically thereto, the second roller 2 has cheek-like convex inwardbulges in regions 6 so that, in side elevation, a type of flat bellshape results in the contour of the second roller 2.

In its central region 7, the first roller 1 features a relative diameterreduction in order to enable an engagement of section 5 of the secondroller 2 in this region and, in addition, leave a comfortable gap 12 asfree space for bending a respectively transported sheet. To achievethis, the first roller 1 essentially has the approximate shape of adumbbell and has on both sides, symmetrically adjacent to central region7, dumbbell heads 8 having a relatively larger diameter. In the regionof said dumbbell heads 8, the first roller 1 has running and run-offpaths 9 for the second roller 2, which, regarding their contour, areapproximately complementary to the cheek-like regions 6 in theirassociate sections. The inventive device deforms a thin sheet 18 in sucha manner that said sheet follows largely the contour of the secondroller 2, as shown in FIG. 1.

FIG. 4 shows the device of FIG. 3 during the transport of a thick sheet13. In FIG. 4, the same components have the same reference numbers as inFIG. 3.

Due to its intrinsic stiffness, the thick sheet 13 is able to lift thesecond roller 2 against a not specifically illustrated application offorce and against the force of the weight of the second roller 2 suchthat thick sheet 13 is transported flat and entirely without being bentbetween rollers 1 and 2. In so doing, thick sheet 13 contacts the convexbulge section 5 of the second roller 2 in said roller's central region,and said sheet moves on the first roller 1 on run-off paths 14 ofdumbbell heads 8, which are located farther outside than run-off paths9.

A sheet of medium thickness would be bent slightly by the second roller2, which would be located slightly lower than in FIG. 4, namely bentless than the extension of the contour of the second roller 2 in FIG. 3and bent more than the thick sheet 13 in FIG. 4, and would then, forexample, roll off on run-off paths 15 of dumbbell heads 8 of the firstroller 1, which are provided between run-off paths 9 and 14. Run-offpaths 9, 14, 15 need not necessarily be discrete and arranged at anangle with respect to each other. Different lines of contact may resultfor sheets having different thicknesses and different curvatures on acontinuously rounded contour of dumbbell heads 8 of the first roller 1.

FIG. 5 shows a third example of embodiment of a second roller 2. Also,in the case of this second roller 2, the associate first roller 1 maycorrespond to the first roller of FIG. 3.

In FIG. 5, only the contour (for example, having the shown dimensions)of the second roller 2 has been drawn. The second roller of FIG. 3 canbe divided virtually (or also reality) into a barrel-like base element10 and a tire-like bead 11, in which case bead 11, may be embodied, forexample, even by a disk or by a tire. In so doing, the contour of thesecond roller 2 has convexly bulging regions, which, however, do notfeature a continuous transition but have sudden diameter increases onthe edges of bead 11.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

Parts List

-   1,2 Rollers-   3, 4 Axles-   5 Section-   6 Regions-   7 Central region-   8 Dumbbell heads-   9 Paths-   10 Element-   11 Bead-   12 Gap-   13 Thick sheet-   14 Path-   15 Path-   16 Double arrow—axial direction in their respective hubs-   17 Double arrow—axle arranged movably-   18 Thin sheet

1. Sheet transport device, preferably for arrangement on thesheet-delivery side of a printing machine, specifically anelectrophotographically operating printing machine, comprising: at leasttwo rollers that are axis-parallel with respect to each other and formbetween them a transport gap for the sheets, the relative distancebetween said rollers being variable in that the rollers and/or zones ofthe rollers can be crossed or staggered relative to each other for areversible deformation and stiffening of sheets respectively transportedbetween them, and a force being applied toward a magnification orincrease of said crossing of the rollers and/or the roller zones, andthe deformation of the sheet being pre-specified, characterized in thatthe rollers are arranged and configured and the application of force isset or selected in such a manner that a sheet which exceeds a specificintrinsic stiffness is able to move the rollers apart against theapplied force in order to avoid said sheet's deformation.
 2. Device asin claim 1, characterized in that the application of force is set orselected relative to a weight per unit area of the sheet.
 3. Device asin claim 2, characterized in that the application of force relative isset or selected relative to the force applied to a sheet having a weightper unit area, which is greater than or approximately equal toapproximately 220 grams per square meter.
 4. Device as in claim 2,characterized in that the application of force is set or selected insuch a manner that a sheet having a weight per unit area of greater thanor approximately equal to 100 grams per square meter is deformed to itsmaximum.
 5. Device as in claim 2, characterized in that one of therollers is driven by a shaft, while the other roller, follows on itsaxle said other roller.
 6. Device as in claim 5, characterized in thatthe follow-roller is subject to the application of pressure in thedirection toward the driven roller.
 7. Device as in claim 2,characterized in that the applied force can be set in such a mannerthat, taking into consideration the inherent weight of the roller towhich the force is applied, said applied force corresponds to a weightof approximately 400 grams.
 8. Device as in claim 2, characterized inthat the two rollers have profiles that are in engagement with eachother in the transport gap, whereby the profile of a first roller has areduced diameter in a central region, while the profile of a secondroller has an enlarged diameter in an approximately corresponding regionsuch that the profile engagement can serve for stiffening a respectivesheet transported through the transport gap.
 9. Device as in claim 8,characterized in that, in order to enlarge the diameter of the secondroller, viewed in side elevation of the second roller, a roundedtransition is implemented in at least one section.
 10. Device as inclaim 8, characterized in that the rollers are configured symmetricallywith respect to a respective diameter extreme.
 11. Sheet transportdevice, preferably for arrangement on the sheet-delivery side of aprinting machine, specifically an electrophotographically operatingprinting machine, comprising: at least two rollers that areaxis-parallel with respect to each other and form between them atransport gap for the sheets, said two rollers having profiles that arein engagement with each other in the transport gap, whereby the profileof a first roller has a reduced diameter in a central region, while theprofile of a second roller has an enlarged diameter in an approximatelycorresponding region such that the profile engagement can serve forstiffening a respective sheet transported through the transport gap,characterized in that, in order to enlarge the diameter of the secondroller, viewed in side elevation of the second roller, a roundedtransition has been implemented in at least one section.
 12. Device asin claim 11, characterized in that, in order to enlarge the diameter ofthe second roller, viewed in side elevation of the second roller, arounded transition is provided at least in respectively one section onboth sides of the diameter maximum.
 13. Device as in claim 12,characterized in that the rollers are configured symmetrical withrespect to a respective diameter extreme.
 14. Device as in claim 13,characterized in that the second roller is essentially slightlybarrel-shaped.
 15. Device as in claim 13, characterized in that thefirst roller has approximately the shape of a dumbbell.
 16. Device as inclaim 13, characterized in that, between the axis-parallel rollers aforce acts in engagement direction, said force being set or selected insuch a manner that a thin sheet is deformed to stiffen it in such amanner that it follows the profile of the second roller.